Sam Jacob

Chloroacetonitrile (CAN) induces glutathione depletion and 8-hydroxylation of guanine bases in rat gastric mucosa.

Chloroacetonitrile (CAN) is detected in drinking‐water supplies as a by‐product of the chlorination process. Gastroesophageal tissues are potential target sites of acute and chronic toxicity by haloacetonitriles (HAN). To examine the mechanism of CAN toxicity, we studied its effect on glutathione (GSH) homeostasis and its impact on oxidative DNA damage in gastric mucosal cells of rats. Following a single oral dose (38 or 76 mg/Kg) of CAN, animals were sacrificed at various times (0–24 h), and mucosa from pyloric stomach were collected. The effects of CAN treatment on gastric GSH contents and the integrity of genomic gastric DNA were assessed. Oxidative damage to gastric DNA was evaluated by measuring the levels of 8‐Hydroxydeoxyguanosine (8‐OHdG) in hydrolyzed DNA by HPLC‐EC. The results indicate that CAN induced a significant, dose‐ and time‐dependent, decrease in GSH levels in pyloric stomach mucosa at 2 and 4 hours after treatment (56 and 39% of control, respectively). DNA damage was observed electrophoretically at 6 and 12 hours following CAN administration. CAN (38 mg/Kg) induced significant elevation in levels of 8‐OHdG in gastric DNA. Maximum levels of 8‐OHdG in gastric DNA were observed at 6 hours after CAN treatment [9.59 ± 0.60 (8‐OHdG/105dG) 146% of control]. When a high dose of CAN (76 mg/Kg) was used, a peak level of 8‐OHdG [11.59 ± 1.30 (8‐OHdG/105dG) 177% of control] was observed at earlier times (2 h) following treatment. When CAN was incubated with gastric mucosal cells, a concentration‐dependent cyanide liberation and significant decrease in cellular ATP levels were detected. These data indicate that a mechanism for CAN‐induced toxicity may be partially mediated by depletion of glutathione, release of cyanide, interruption of the energy metabolism, and induction of oxidative stress that leads to oxidative damage to gastric DNA.

Studies on the mechanism of haloacetonitriles toxicity : quantitative whole body autoradiographic distribution of [2-14C]chloroacetonitrile in rats

Chloroacetonitrile (CAN), a drinking water disinfectant by-product, possesses mutagenic and carcinogenic properties. The objective of this study was to investigate the biologic fate of CAN, using whole body autoradiographic (WBA) techniques. Male Sprague-Dawley rats were treated with a tracer dose of [2-14C]CAN (i.v., 88 muCi/kg, spec. act 4.07 mCi/mmol). At various time intervals (0.08, 1, 3, 6, 12, 24, and 48 h) after treatment, rats were processed for WBA. Over 12 h after administration, the radioactivity excreted in urine, feces, and exhaled as 14CO2 accounted for 51%, 2.7%, and 12% of the dose, respectively. Only 0.8% of the administered dose was exhaled as unchanged CAN. At an early time interval (5 min) extensive accumulation of radioactivity was observed in liver, kidney, and gastrointestinal (G.I.) walls. In addition, high levels of 14C were detected in the thyroid gland, lung bronchioles, adrenal cortex, salivary gland, and testes. At 1 h following administration, the olfactory bulb, olfactory receptor area of the brain and lumbar cistern showed high accumulations of radioactive CAN or its equivalents. At 3, 6, and 12 h after treatment, the radioactivity diffused homogeneously in all tissues and reconcentrated in several organs at later time periods (24 and 48 h). Our studies indicate extensive metabolic biotransformation of CAN in rats. The retention of radioactivity in the tissues of the thyroid gland, G.I., testes, brain and eye suggest that those organs are potential target sites of CAN toxicity.

Effect of Glutathione Modulation On the Distribution and Transplacental Uptake of 2-[14C]-Chloroacetonitrile (Can) Quantitative Whole-Body Autoradiographic Study in Pregnant Mice

Chloroacetonitrile (CAN), a drinking water disinfectant by-product, has mutagenic and carcinogenic properties. CAN is known to deplete glutathione (GSH), and previous studies reported an enhanced molecular interaction of CAN after GSH depletion in the uterine and fetal tissues of mice. The present report may help to understand the potential mechanisms involved in such molecular interactions by examining the disposition, transplacental uptake and covalent interaction of the chemical in normal and GSH depleted pregnant mice (at 13th day of gestation). Both normal and GSH depleted (by administration of Diethylmaleate (DEM), 0.6 mL/kg, i.p.) pregnant mice were given an equitoxic i.v. dose of 2-[14C]-CAN (333 μCi/kg equivalent to 77 mg/kg). Animals were processed for whole-body autoradiography (WBA) at 1, 8 and 24 hr after treatment. Tissue distribution of radioactivity in the autoradiographs was quantitated using computer aided image analysis. With few exceptions, a rapid high uptake (at I hr) of radioactivity was observed in all major maternal (liver, lung, urinary bladder, gastrointestinal mucosa, cerebellum, uterine luminal fluid) and fetal (liver, brain) organs of both normal and GSH depleted mice. This pattern of distribution was observed, with lesser intensity, at 8 hr following treatment. At a later time period (24 hr), there was a significant higher retention and covalent interaction of radioactivity in GSH depleted mouse tissues especially in the liver as compared to normal mouse. This study suggests that 2-[14C]-CAN and/or its metabolites are capable of crossing the placental barrier. The observed higher uptake and retention of the radioactivity in the maternal liver, kidney, cerebellum, nasal turbinates and fetal liver may pose toxicity of the chemical to these organs. The increased covalent interaction of radioactivity in GSH depleted mice liver may indicate the potential utilization of GSH pathway by this organ in the detoxication of CAN derived metabolites and thus exerting hepatotoxicity.

Role of calcitonin gene-related peptide (CGRP) in ovine burn and smoke inhalation injury

Concomitant smoke inhalation trauma in burn patients is a serious medical problem. Previous investigations in our sheep model revealed that these injuries lead to significant airway hyperemia, enhanced pulmonary fluid extravasation, and severely impaired pulmonary function. However, the pathophysiological mechanisms are still not fully understood. The lung is innervated by sensory nerves containing peptides such as substance P and calcitonin gene-related peptide. Noxious stimuli in the airways can induce a neurogenic inflammatory response, which has previously been implicated in several airway diseases. Calcitonin gene-related peptide is known to be a potent vasodilator. We hypothesized that calcitonin gene-related peptide is also a mediator of the pulmonary reaction to toxic smoke and planned experiments to evaluate its role in this model. We tested the effects of pretreatment with a specific antagonist of the major receptor for calcitonin gene-related peptide (BIBN4096BS; 32 microg/kg, followed by continuous infusion of 6.4 microg.kg(-1).h(-1)) until the animal was killed 48 h after injury in an established ovine model of burn (40% total body surface, third degree) and smoke inhalation (48 breaths, <40 degrees C) injury. In treated animals (n = 7), the injury-related increases in tracheal blood flow and lung lymph flow were significantly attenuated compared with untreated controls (n = 5). Furthermore, the treatment significantly attenuated abnormalities in respiratory gas exchange. The data suggest that calcitonin gene-related peptide contributes to early airway hyperemia, transvascular fluid flux, and respiratory malfunction following ovine burn and smoke inhalation injury. Future studies will be needed to clarify the potential therapeutic benefit for patients with this injury.

Pulmonary expression of nitric oxide synthase isoforms in sheep with smoke inhalation and burn injury.

Previous studies have indicated increased plasma levels of inducible nitric oxide synthase in lung. This study further examines the pulmonary expression of nitric oxide synthase (NOS) isoforms in an ovine model of acute lung injury induced by smoke inhalation and burn injury (S+B injury). Female range bred sheep (4 per group) were sacrificed at 4, 8, 12, 24, and 48 hours after injury and immunohistochemistry was performed in tissues for various NOS isoforms. The study indicates that in uninjured sheep lung, endothelial (eNOS) is constitutively expressed in the endothelial cells associated with the airways and parenchyma, and in macrophages. Similarly, neuronal (nNOS) is constitutively present in the mucous cells of the epithelium and in neurons of airway ganglia. In uninjured lung, inducible (iNOS) was present in bronchial secretory cells and macrophages. In tissue after S+B injury, new expression of iNOS was evident in bronchial ciliated cells, basal cells, and mucus gland cells. In the parenchyma, a slight increase in iNOS immunostaining was seen in type I cells at 12 and 24 hours after injury only. Virtually no change in eNOS or nNOS was seen after injury.

Acrylonitrile-induced neurotoxicity in normal human astrocytes: oxidative stress and 8-hydroxy-2'-deoxyguanosine formation.

Studies in our laboratory and others have indicated that acrylonitrile (VCN) induces acute and chronic neurotoxicity and brain tumors in animal models. Reduced glutathione (GSH) depletion was suggested as the initiator of oxidative stress in VCN-induced neurotoxicity. Astrocytes possess the majority of total brain GSH and express various immunological functions that are characteristic of the brain, including the secretion of cytokines. We hypothesized that astrocytes could be the primary target of VCNs adverse activities in the brain. Therefore, VCN-induced neurotoxicity was studied by exposing proliferating normal human astrocytes (NHAs) to various concentrations of VCN (25-400 μM). We assessed cell viability; levels of endogenous antioxidants, GSH, and catalase; levels of reactive oxygen species; and secretion of TNF- α, a cellular marker for oxidative stress and oxidative damage to nuclear DNA, after treatment with VCN. At VCN concentrations of 25 and 50 μM, the oxidative stress markers were unaffected and at least 85% of the cells were viable. Cell viability was significantly affected at 200 and 400 μM VCN (22-42% less than control, p <. 05). The results also indicated VCN-induced depletion of GSH and a concomitant increase in levels of oxidized GSH (GSSG). The levels of total GSH and GSSG in control and treated (400 μM VCN) cells were 37 and 2, respectively. There was a significant upregulation of catalase activity (21% more than control, p <. 05) at 100 μM of VCN and a downregulation at 400 μM (40% lower than control, p <. 05). A dose-dependent, significant increase in the formation of reactive oxygen species was observed at 200 to 400 μM of VCN. Also, an elevation (two- to three fold as compared to control, p <. 05) in oxidative damage to DNA was observed at these concentrations of VCN. Increase in TNF- αsecretion (28% higher than control, p <. 05) was observed at 400 μM VCN. Therefore, redox imbalance in astrocytes may play a major role in VCN-induced neurotoxicity, which is indicated by compromised antioxidant defense mechanisms, such as depletion of GSH, increase in GSSG, inhibition of catalase, and increase in the formation of reactive oxygen species and TNF- αsecretion, resulting in DNA oxidation.

Activated nuclear factor kappa B and airway inflammation after smoke inhalation and burn injury in sheep.

In a recent study, we have shown a rapid inflammatory cell influx across the glandular epithelium and strong proinflammatory cytokine expression at 4 hours after inhalation injury. Studies have demonstrated a significant role of nuclear factor kappa B in proinflammatory cytokine gene transcription. This study examines the acute airway inflammatory response and immunohistochemical detection of p65, a marker of nuclear factor kappa B activation, in sheep after smoke inhalation and burn injury. Pulmonary tissue from uninjured sheep and sheep at 4, 8, 12, 24, and 48 hours after inhalation and burn injury was included in the study. Following immunostaining for p65 and myeloperoxidase, the cell types and the percentage of bronchial submucosal gland cells staining for p65 and the extent of myeloperoxidase stained neutrophils in the bronchial submucosa were determined. Results indicate absence of detection of P65 before 12 hours after injury. At 12 hours after injury, strong perinuclear staining for p65 was evident in bronchial gland epithelial cells, macrophages, and endothelial cells. Bronchial submucosal gland cells showed a significant increase in the percentage of cells stained for p65 compared with uninjured animals and earlier times after injury, P < .05. At 24 and 48 hours after injury, p65 expression was evident in the bronchiolar epithelium, Type II pneumocytes, macrophages, and endothelial cells. Quantitation of the neutrophil influx into the bronchial submucosa showed a significant increase compared with uninjured tissue at 24 and 48 hours after injury, P < .05. In conclusion, immunohistochemical detection of activated p65 preceded the overall inflammatory response measured in the lamina propria. However, detection of p65 did not correlate with a recent study showing rapid emigration of neutrophils at 4 hours postinjury. Together, these results suggest that p65 immunostaining may identify cells that are activated to produce proinflammatory cytokines after injury; however, the immunoexpression may not adequately reflect the temporal activation of gene transcription that may occur with proinflammatory cytokine production with inhalation injury.

Acute secretory cell toxicity and epithelial exfoliation after smoke inhalation injury in sheep: An electron and light microscopic study

Smoke inhalation injury promotes exfoliation of the upper airway columnar epithelium. Tracheal tissues from sheep 30 min after smoke exposure show intact epithelial areas, areas of epithelial disruption with loss of columnar cells and areas denuded of columnar cells. In intact areas detaching ciliated cells can be seen raised above the apical surface. This study aims to assess cell-specific toxicity by examining intact epithelium after inhalation injury. The junctional adhesion integrity between columnar and basal cells and the type of cells initially being displaced were also studied using light (LM) and transmission electron microscopy (TEM). TEM assessment of intact areas of sheep tracheal tissue (n = 3) 30 min after exposure showed secretory cell toxicity including extrusion of cytoplasmic contents. In cells with severe secretory cell cytoplasmic disruption, loss of desmosomal junctions between the secretory and adjacent ciliated cells was evident. The number of desmosomes visible between columnar cells and basal cells was reduced (2.8 ± 1.8) in smoke-exposed animals compared to those in uninjured animals (5.0 ± 2.7), p = 0.008. Serial sections of intact regions found 52 cells being displaced from the epithelium. All detaching cells were identified as ciliated cells. These studies show that the acute effects of inhalation injury include selective secretory cell toxicity which is associated with loss of junctional adhesion mechanisms and displacement of ciliated cells. Improved understanding of acute hypersecretory responses and epithelial integrity after exposure to toxic agents may improve understanding of epithelial fragility in airway disease.

Muscarinic receptor antagonist therapy improves acute pulmonary dysfunction after smoke inhalation injury in sheep.

Objectives:Inhalation injury contributes to the morbidity and mortality of burn victims. In humans and in an ovine model of combined smoke inhalation and burn injury, bronchospasm and acute airway obstruction contribute to progressive pulmonary insufficiency. This study tests the hypothesis that muscarinic receptor antagonist therapy with tiotropium bromide, an M1 and M3 muscarinic receptor antagonist, will decrease the airway constrictive response and acute bronchial obstruction to improve pulmonary function compared to injured animals without treatment. Design:Randomized, prospective study involving 32 sheep. Setting:Large-animal intensive care research laboratory. Interventions:The study consisted of six groups: a sham group (n = 4, instrumented noninjured), a control group (n = 6, injured and not treated), and tiotropium bromide-treated groups, including both preinjury and postinjury nebulization protocols. Treatments for these groups included nebulization with 36 &mgr;g of tiotropium bromide 1 hr before injury (n = 6) and postinjury nebulization protocols of 18 &mgr;g (n = 6), 36 &mgr;g (n = 6), and 72 &mgr;g (n = 4) administered 1 hr after injury. All treated groups received an additional 14.4 &mgr;g every 4 hrs for the 24-hr study period. Main Results:Pretreatment with tiotropium bromide significantly attenuated the increases in ventilatory pressures, pulmonary dysfunction, and upper airway obstruction that occur after combined smoke inhalation and burn injury. Postinjury treatments with tiotropium bromide were as effective as pretreatment in preventing pulmonary insufficiency, although a trend toward decreased obstruction was present only in all post-treatment conditions. There was no improvement noted in pulmonary function in animals that received a higher dose of tiotropium bromide. Conclusions:This study describes a contribution of acetylcholine to the airway constrictive and lumenal obstructive response after inhalation injury and identifies low-dose nebulization of tiotropium bromide as a potentially efficacious therapy for burn patients with severe inhalation injury.

Effect of route of administration on the disposition of acrylonitrile: quantitative whole-body autoradiographic study in rats

Previous studies on the effect of route of administration on acrylonitrile (VCN) toxicity in animal models indicated high rates of metabolism in rats that received an oral dose than those received an i.p. VCN dose. To evaluate the role of route of administration on the distribution of VCN, a quantitative whole-body autoradiography (QWBA) and elimination studies were conducted. Equimolar doses of 2-[14C]-VCN were administered i.v. or p.o. to male Fischer (F-344) rats. Time course of QWBA indicated a higher retention and covalent interaction of radioactivity in the liver, spleen and bone marrow of rats received an i.v. dose of 2-14C-VCN than those received a p.o. dose. Unlike rats that received an i.v. dose of VCN, the animals received an oral dose showed a high retention of 14C in blood, stomach and gastric mucosa. Differences were also reflected in 14C elimination in urine, feces and expired air. Animals treated orally with 2-[14C]-VCN excreted 61% of the administered radioactive dose (4% in expired air, 4% in urine and 53% in feces). Rats that received an i.v. dose of 2-[14C]-VCN, however, eliminated only 30% of the total radioactive dose (expired air 2%, urine 8% and feces 21%). The results indicate that metabolism, detoxication and elimination of VCN are more pronounced following oral administration as compared to i.v. route of administration. The study also demonstrates that the systemic administration of VCN enhances its covalent interaction and retention in the tissues thus cause more toxicity in these organs.